1. Field of the Invention
This present invention is directed to blowout preventers, to bonnets for them, to supports for such bonnets, and, in certain particular aspects, to pivotal bonnet supports, and methods of their use.
2. Description of Related Art
The prior art discloses a wide variety of blowout preventers and blowout preventer bonnets. Typically, a blowout preventer is used in oil and gas well operations to seal a wellbore. Fluids or gas in a formation, through which a wellbore extends exert increasing pressure with increasing formation depth. This pressure can affect the wellbore and equipment associated with the wellbore. Drilling fluid density can be adjusted to balance a formation's fluid's pressure and/or pump pressure can be increased at a surface of the well to pump fluid at a desired pressure to balance pressure.
If formation pressure is encountered that is higher than the pressure maintained in the wellbore, sometimes referred to as a “kick,” this pressure can move uphole and damage equipment at the surface causing a “blowout.” A blowout can produce severe damage, personal injury, and death.
Blowout preventers are used at the surface (or on a sea floor) to immediately and automatically control kicks and prevent blowouts until other procedures can be employed to deal with the well. The prior art includes both annular blowout preventers and ram-type blowout preventers.
Typical annular blowout preventers have selectively actuatable annular elastomer members which encompass pipe and/or tools and seal off a wellbore. Typical ram-type blowout preventers have a body and at least two oppositely disposed bonnets secured to the body which, in certain prior art systems, are movably secured with movable bars or with hinges and bolts so that the bonnet is movable for access and maintenance. Certain prior art bonnets contain a piston actuated ram which is either a pipe ram (to contact, engage, and encompass pipe and/or tools to seal a wellbore) or shear rams (to contact and physically shear a pipe or tool in a wellbore). Rams are usually positioned opposite each other on either side of a main body and can seal against each other at a center of the main body over a center of a wellbore.
High pressure elastomer seal elements used on blowout preventer rams are regularly inspected and maintained. Such seals can be subject to high pressures and to chemical reaction with drilling fluids which can damage the seals. Often rams are inspected or changed out. Prior art systems include a variety of movable bonnets for accessing rams and seals.
U.S. Pat. Nos. 5,897,094 and 5,975,484, co-owned with the present invention, disclose an improved blowout preventer door connection that includes connector bars for securing bonnets to a blowout preventer.
U.S. Pat. Nos. 6,510,897 and 6,554,247 and U.S. patent applications Ser. Nos. 10/322,038 filed Dec. 17, 2002 and 10/424,698 filed Apr. 28, 2003 disclose rotational mounts for blowout preventer bonnets.
In certain typical ram-type blowout preventers hydraulically actuated cylinders with one or more pistons interconnected to respective rams via a shaft move the rams to shear pipe and sealing a bore (in a shear ram blowout preventer) or move pipe rams for sealing around pipe (in a pipe ram blowout preventer). Certain typical ram actuators disposed in a bonnet have one or more pistons and cylinders connected in a hydraulic circuit with an hydraulic fluid source that provides fluid under pressure to move the piston(s) within the cylinder.
Significant forces are applied to shear a pipe. In certain prior art systems a booster piston and cylinder add force to a primary operating piston and cylinder and the combined forces are applied to rams that shear pipe and seal off a bore. The force required for shearing a pipe is much greater than the force needed to seal an open bore after the pipe has been sheared. If the total ram force used to shear the pipe is applied to the seals on the ram, the seals can be damaged. In certain prior art systems the operating piston force on the seals is reduced after the rams have sheared a pipe; but the hydraulic pressure on such operating pistons can remain at the same high level during both the shearing and sealing operations. Blowout preventers are disclosed in many U.S. Patents, including, but not limited to, U.S. Pat. Nos. 3,946,806; 4,043,389; 4,313,496; 4,132,267, 4,558,842; 4,969,390; 4,492,359; 4,504,037; 2,752,119; 3,272,222; 3,744,749; 4,253,638; 4,523,639; 5,025,708; 5,056,418; 5,400,857; 5,575,452; 5,653,418; 5,655,745; and 5,918,851.
There has long been a need, recognized by the present inventors for a blowout preventer with a bonnet which is movable and stable during movement and which provides easy access to rams within the blowout preventer.
There has long been a need, recognized by the present inventors for apparatus for moving a bonnet which requires a minimum of space and for a blowout preventer with such apparatus that has a minimal footprint.